1. Field of the Invention
This invention relates to a method of recovery of single cell protein (SCP) from food wastes. More particularly, this invention relates to a method of recovery of protein from food wastes in which a medium composed of various combined food wastes and containing both a protein source and a carbohydrate source is modified by the action of selected microbial species. The resulting modified liquid medium permits the growth of more fastidious organisms that are acceptable as a single cell protein source. The final recovery of protein from the fastidious organisms may be accomplished by any one of the established methods of protein or food recovery and/or isolation. Single cell protein is used as a protein additive or supplement for food for human use and as an animal feed and feed supplement.
2. Description of the Prior Art
The only materials produced industrially as single cell protein (SCP), at present available to the commercial animal feed industry, are those derived from hydrocarbon grown yeasts. While these processes produce SCP of demonstrably high quality, the methanol and the various hydrocarbons used in these processes are not waste materials. In fact, they are very useful products having high priority utility in energy production and other industrial fields.
In a recent paper (Bough et al, 1972, App. Microbiol. 24:2: 226-235), there is described a means of producing single cell protein from collagenous by-products of the meat industry through the continuous cultivation of Bacillus megaterium. The protein obtained from the B. megaterium cells was found to be superior to the collagen from a nutritional standpoint. An improved amino acid balance and higher protein efficiency ratio were evidence of this. This is a one step process using only one organism to ferment only one substrate.
Many of the processes for the utilization of complex carbohydrates such as starch or cellulose involve the use of two or more fermenting organisms. The first fermentation breaks down the complex carbohydrate into simpler sugars which can be used in the secondary fermentation for the production of single cell protein. The proposed process belongs to this general area of single cell protein manufacture.
One such process is the symba yeast process described by Lars Emmelin (Emmelin, L. 1974. Environmental Planning in Sweden N. 52. Protein from Waste Water. Current Sweden 52). Starch containing waste water from potato processing plants is fermented by a mixed culture containing a fungus, Endomycopsis fibuliger and a Candida yeast. The fungus produces amylases which hydrolyze the starch giving simpler sugars which can be fermented by the yeast. The yeast, which is the only product of the system, is considered a good source of protein.
Another process which depends on the action of fungal enzymes to hydrolyze complex carbohydrate molecules is the "koji fermentation," described in two papers by Professor Wm. Stanton (Stanton, W. R. et al, 1969. Process Biochem. 5:4:45-51 and Stanton, W. R. 1972. Process Biochem. 7:2.) It has been adapted by others (Kassai, P. T. et al, 1973. Adaptation of the "koji fermentation" to Waste Disposal. Abstracts of the Annual Meeting of the ASM. 73,3. and Savage, J. et al. 1973. Growth of Candida utilis on Chemical, Microbial and Enzymatic Hydrolysates of Swine Waste. Abstracts of the Annual Meeting of the ASM. 73.). This fermentation consists of an aerobic enzyme producing stage (koji) followed by an anaerobic aqueous phase (moromi) in which the enzymes catalyze degradation of the complex molecules found in the original waste materials. While this process is normally applied to the fermentation of rice and other starchy materials in the Orient for the production of fermented food products, both of these groups adapted the process to the degradation of animal fecal wastes for the production of single cell protein.